I was given a Toro 521 Snowblower. It won't start. I replaced the plug, gas filter, air filter and gas line. Still won't start. Also drained the tank and added new gas

Re-check the carb... esp the float valve...
Did you seen this YOUTUBE?

Engine Won Start Snowblower Troubleshooting

Hi Jerome:
Shouldn't be too bad.
You could disconnect the fuel line at the carb and drain the tank.
Drain and flush the carb. Reconnect the fuel line and fill with fresh gas.
If it won't start, pull the spark plug and clean/dry it with a propane torch, or replace it.
Odds are it will be fine.
Cheers.

Is it coming from the carb or tank? Either way replace the fuel lines, they crack an get pin holes in them an cause problems. If it comes from the carb get a rebuild kit an, very cheap, an replace the seals.

Check the fuel line to the tank, and see if another one is inside, maybe it fell off, or it's filter is clogged.

Ensure gas tank only has fresh gas with Stabile. Replace spark plug and air filter. Fill oil. 30w.Ensure primer bulb is not cracked.

Clean the carb, gas tank and fuel line (s). Replace air filter with a new one, I wouldn't recommend that you run it without the filter because that allows dirt and grass debri to enter the carb, fuel line and gas tank.
Replace the plug with a new one that is recommended for your engine.
Check oil level.

Other option is lawn mower repair shop....

Hope this helps, I had the same problem.

Not a big deal. Im assuming this is a 4-stroke push mower and not a leaf blower.
Remove the air box cover, air filter, and air box back plate. Careful there is a gasket on the back of the backplate that if damaged the primer bulb wont work, part # 272653. Remove the fuel line from the carb and drain the tank. Using a 1/2 inch wrench remove the bowl nut from the float bowl on the carb, hold the bowl to the carb as to not break the gasket seal, drain the bowl and replace the bowl nut. If you tried to run the unit and oil is in the cylinder remove the spark plug ( clean the spark plug) and spray some carb cleaner in the hole and pull the starter rope several times to purge the cylinder. Reinstall the spark plug, reattatch the fuel line, install the air box back plate ( leave the air filter and cover off for now), add fresh fuel.
Take unit outside and start, you may need to give it a shot of carb cleaner in the throat of the carb to help it start. It may smoke, it may blow oil out the muffler. Let it run until it quits smoking ( usually around 5 minutes) . Shut it off and complete assembly. It should be fine.

Or, you can try the easy approach. Take a 1/4" bolt about 2" long and cutoff the head. Force the bolt into the old fuel line on the fuel tank side (after removing fuel tank), push other end into new fuel line, tape the lines together well with electrical tape. Gently pull from one side and push from the other until new section of line comes through. Just did this and it too all of 5 minutes.

I am not sure what type of carb you have so I will give you a couple of ideas.
1. If the carb is one of the plastic ones that attaches directly to the gas tank take of the air cleaner and press the primer bulb. If you get a spurt of gas and not a stream of gas get a new diaphragm for the carb. It goes between the tank and the carb.
2. If there is a sediment bulb hooked to the carb drain the gas from tank and then carefully remove the sediment bulb and clean it.
3. If there is a sediment bulb hooked to the carb and a flat paper air filter attached to the sediment bulb via a plastic air filter holder with a primer bulb built into the air filter holder replace the gasket between filter cover and sediment bulb.

good luck
let me know if this works.
roundo4

Remove your fuel filter (in the tank usually) and, replace it